I'm sorry, but exactly what did you fix?
Forums are now automatically created when the language is still in English. Translations of "Hidden", "per page discussions", "deleted threads", etc cannot be used. This no different than changing site language back to English, then activating forums. You just automated that step. This is just a workaround to eliminate the 500 error, not a real fix. It's useless.

I made a test on testdeutsch1 site:http://testdeutsch1.wikidot.com
and on forum there was no possibility anymore to activate it.
( as you have written)
==> But there was no one group and category by default existent
I has to make it manually - ok , I know what i am doing -

createwd
1. hidden group
1.1 hidden threads
1.2. per page discussionsss ( the are needed I think?
and a standard forum ..

Than I created a coment on the start site - intersting if teh own keyed in "per page discusssionssss" category will be used or a new one generated.

http://testdeutsch1.wikidot.com/forum/start
shows - a new one is generated ( ok, this is understandable.
This works as it should… ( we can rewrite all howtos's now)
Bad is the fact - there is no hidden grioup with hiden threads anymore!

Now that forums are activated automatically for new sites, I would suggest that the following categories be there by default:

General Discussion (Public)
Per Page Discussion (Hidden)

And the permissions by default should be that all site members can post in the General Discussion section.

That way, discussions can be started immediately, without the site admin having to go into the site manager and set up the forum structure.

One trap I continually fell into was to activate my forum, but forget to set up the forum structure - so I had to return to the site manager to fix this. If I keep forgetting to do it, I'm sure new users certainly will! ;-)